This invention relates to a method of manufacturing tasty and aromatic roasted coffee beans and ground roasted coffee beans.
The following is one of the prevailing methods of manufacturing roasted coffee beans and ground roasted coffee beans.
a. Roasting
Coffee beans are roasted in a hot blast drum roaster for about 10 minutes with the hot blast temperature between 400.degree. and 500.degree. C. The temperature of the coffee beans is approximately 200.degree. C. immediately after the roasting.
b. Cooling
The roasted coffee beans are air-cooled for about 5 minutes to room temperature (approximately 20.degree. C.).
c. Blending
Several varieties of roasted coffee beans are blended.
d. Grinding
The blended coffee beans are ground, if desired.
e. Degasification
The roasted (and ground) coffee beans are stored in an airtight silo for 12 hours to 4 days for carbon dioxide degasification.
f. Packaging
The roasted coffee beans obtained at step (d) or the ground coffee beans at step (e) are packaged preferably in airtight containers.
The commercially available coffee beans manufactured according to the above method gradually deteriorate during storage, causing loss of the fresh rich flavor. Much of the rich flavor of coffee, attributable to the various chemical components produced by roasting, is lost by dispersion and change of the chemical components occurring after roasting. Volatile chemical components in the beans will be dispersed and lost as time passes while oxidation and other chemical changes will also occur, all contributing to the loss of flavor.
Even with improved packaging methods such as nitrogen gas replacement and vacuum packaging to prolong the shelf life, the flavor of coffee deteriorates fairly rapidly at room temperature. The process is intensified in the case of ground beans so that storage for weeks to months will result in substantial deterioration. Once a package is opened, loss and deterioration of the fresh flavor is particularly rapid. This is further intensified if the storage period has been long before opening the package. It is known that keeping roasted coffee beans at a low temperature is partially effective in preserving the fresh flavor. However, this low temperature storage method, though achieving limited success, does not significantly arrest the process of deterioration. For example, the loss/deterioration rate of coffee stored at 5.degree. C. is only about one third of coffee stored at 25.degree. C.
Other problems inherent in the above conventional manufacturing method include dispersion and loss of aromatic components caused by post-roasting residual heat, uneven secondary roasting also caused by post-roasting residual heat, and dispersion and loss of aromatic components caused by the heat generated while grinding roasted beans.
Among conventional manufacturing methods that freeze roasted beans below -17.degree. C., the prevailing method comprises freezing roasted coffee beans by liquid nitrogen or some other inert gas or fluid before grinding to prevent dispersion and chemical change of aromatic the components. Japan Published Unexamined Patent Application No. S47-20371 discloses one such method, in which roasted coffee beans are ground after being frozen to -25.degree. to -85.degree. C. by liquid nitrogen injection.
There are other known freezing methods applicable to manufacturing instant coffee and coffee beverages, although, they are not directly related to the object and the method according to the present invention. Japan Published Unexamined Patent Application No. S52-117471 discloses pulverizing roasted beans after freezing the beans to a range of from -79.degree. to -196.degree. C. Japan Published Examined Patent Application No. S60-25100 (Japan Published Unexamined Patent Application No. S57-208947) discloses, in an ordinary method, freezing and pulverizing roasted beans impregnated with polyatomic alcohol. Japan Published Examined Patent Application No. S61-32944 (Japan Published Unexamined Patent Application No. S55-26887) discloses freezing beans with liquid nitrogen and pulverizing them to 45 microns or less. All three methods include the steps of pulverizing roasted beans into particles with a diameter of the order of tens of microns and adding the obtained particles to instant coffee obtained in ordinary manufacturing methods.
Although effectively preserving aromatic components, the above freezing methods are not suitable as methods of manufacturing ordinary roasted coffee beans because of the expensive, complex apparatuses required for using liquid nitrogen which raises the manufacturing costs.